I would like to know how to hook up extra fans to my boiler so that they come on when the thermostat calls for heat and turns off when done.

You better supply a lot more info since I have no idea what you are talking about.

I have a boiler and want to put fans into the system so that they come on when the thermostat calls for heat. These fans would blow the heat around a little more than just having the heat rise from the baseboard.

Just buy a cheap box fan for 19.95 at the store and turn it on low. Baseboard is the best heat going I have no idea why you would want to blow it around but you could also install a ceiling fan which would be better than the box fan.